The present invention relates to an air compressor which is driven by switching a load operation and a no-load operation and a method of operating the air compressor, and more particularly to a screw type air compressor capable of adjusting the capacity thereof and a method of operating the screw type air compressor.
A conventional capacity adjusting apparatus of a air compressor is such that an intake passage and a discharge ventilating passage are independently provided, and valve bodies are provided in the respective passages, as described in JP-A-5-10285, for example. Further, in order to simultaneously operate these two valve bodies, a rack and pinion or the like is employed.
Since the apparatus described in JP-A-5-10285 mentioned above is provided with the intake passage and the discharge ventilating passage independently, so that the apparatus requires a large number of parts such as valve bodies, shafts supporting the valve bodies, shaft seals, bearings for the respective passages, and further requires pipes and silencer apparatus between the intake passage and an air take-in port and between the discharge ventilating passage and the air take-in port respectively, the apparatus has disadvantages such that the cost is increased and the reliability is deteriorated.
In view of the disadvantages in the prior art mentioned above, it is an object of the present invention to provide a screw type air compressor which is inexpensive and has high reliability. Another object of the present invention is to improve reliability of a capacity adjusting apparatus of a screw type air compressor so as to provide an air compressor having high reliability.
According to one aspect of the present invention, there is provided an air compressor comprising a compressor main body, an intake pipe connected to an intake side of the compressor main body and provided with a capacity adjusting apparatus for adjusting the flow of intake air flowing into the compressor main body, and a discharge pipe communicating with a discharge side of the compressor main body, wherein the intake pipe and the discharge pipe are adjacent to each other, a communicating passage is formed in the adjacent portion for introducing the compressed air from the discharge pipe into the intake pipe, an opening port is formed in the intake pipe for limiting the inflow of the intake air into the compressor main body, and the capacity adjusting apparatus comprises an opening and closing means for opening and closing the communicating passage and the opening port at one end portion of the opening and closing means.
In the air compressor mentioned above, the compressor main body may be a screw compressor comprising a male rotor and a female rotor, and/or the opening and closing means may comprise a shaft capable of reciprocating, an opening port switch valve and a communicating port switch valve mounted on one end side of the shaft.
According to further aspect of the present invention, there is provided a method of operating an air compressor comprising a compressor main body, and a capacity adjusting apparatus provided on an intake side of the compressor main body, the air compressor repeating a load operation and a no-load operation using the capacity adjusting apparatus so as to generate compressed air in accordance with the consumption of the compressed air, comprising the steps of:
(a) moving an opening and closing means provided in the capacity adjusting apparatus so as to introduce intake air into an intake side flow passage of the compressor main body and prevent the compressed air discharged from the compressor main body from flowing into the intake side flow passage during the load operation; and
(b) moving the opening and closing means so as to prevent the intake air from flowing into the compressor main body and introduce the compressed air discharged from the compressor main body into the intake side flow passage during the no-load operation.
The method of operating an air compressor mentioned above may further comprise the steps of:
(c) driving the compressor main body by means of an inverter so as to control the rotational speed during the load operation, and
(d) switching the load operation to the no-load operation when the rotational speed of the compressor main body is reduced to a predetermined lower limit value during the load operation.
According to another aspect of the present invention, there is provided a method of operating an air compressor comprising a compressor main body and a capacity adjusting apparatus, wherein the on-off actions for intake air flowing into the compressor main body and discharge air discharged from the compressor main body are controlled substantially at the same for switching a load operation and a no-load operation of the air compressor, comprising the steps of:
(a) turning off the discharge air flowing into an intake side and turning on the intake air flowing into the compressor main body by means of a capacity control apparatus during the load operation, and
(b) turning on the discharge air flowing into the intake side and turning off the intake air flowing into the compressor main body by means of the capacity control apparatus during the no-load operation.
According to still another aspect of the present invention, there is provided an air compressor comprising a capacity adjusting apparatus provided on an intake side thereof, which repeats a load operation and a no-load operation, the capacity adjusting apparatus being provided with an intake port and a discharge ventilating port, the intake port being opened during the load operation and closed during the no-load operation, the discharge ventilating port being closed during the load operation and opened during the no-load operation, wherein the capacity adjusting apparatus comprises a first valve body for opening and closing the intake port and a second valve body for opening and closing the discharge ventilating port, the first valve body and the second valve body are arranged on a integral shaft, and a communicating portion is provided for connecting an intake passage provided on the intake side of the air compressor and a discharge ventilating passage provided on a discharge side of the air compressor.
In the air compressor mentioned above, the first valve body and the second valve body may be integrated in one body. In addition, the capacity adjusting apparatus may comprise the integral shaft having the integrated valve body mounted on one end side thereof and a piston mounted on the other end side thereof, the piston may constitute a hydraulic piston portion together with a casing accommodating the piston, and an atmospheric releasing portion may be provided between the hydraulic piston portion and the intake passage. Further, the hydraulic piston portion, the atmospheric releasing portion, the intake passage and the discharge ventilating passage may be arranged in order; and an air take-in passage may be provided between the intake passage and the discharge ventilating passage. Alternatively, the air compressor may be a screw compressor comprising a pair or two pairs of female and male rotors.
A description of an embodiment of the present invention will be given below with reference to the accompanying drawings.